Low profile fastening assembly

ABSTRACT

A fastener assembly that can be used for the fixation or anchoring of orthopedic devices or instruments to bone tissue. In particular, a low profile variable angle or fixed angle fastener assembly is able to securely connect the orthopedic device to bone tissue. The fastener assembly may have a locking mechanism that will quickly and easily lock the fastener assembly with respect to the orthopedic device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/877,177, filed on Oct. 7, 2015, which is a continuation of U.S.patent application Ser. No. 14/645,466, filed Mar. 12, 2015 (now issuedas U.S. Pat. No. 9,179,953), which is a divisional of U.S. patentapplication Ser. No. 14/103,556 filed on Dec. 11, 2013 (now issued asU.S. Pat. No. 9,005,258), which is a continuation of U.S. patentapplication Ser. No. 12/716,523 filed on Mar. 3, 2010 (now issued asU.S. Pat. No. 8,632,575). The contents of these prior applications arehereby incorporated by reference in their entities for all purposes.

FIELD OF THE INVENTION

The present invention is directed to a bone fixation assembly and, inparticular, to low profile fastening assembly for securing an orthopedicdevice to bone tissue.

BACKGROUND OF THE INVENTION

As is known in the field of orthopedic surgery, and more specificallyspinal surgery, orthopedic fasteners may be used for fixation or for theanchoring of orthopedic devices or instruments to bone tissue. Anexemplary use of fasteners may include using the fastener to anchor anorthopedic device, such as a bone plate, a spinal rod or a spinal spacerto a vertebral body for the treatment of a deformity or defect in apatient's spine. Focusing on the bone plate example, fasteners can besecured to a number of vertebral bodies and a bone plate can beconnected to the vertebral bodies via the bone anchors to fuse a segmentof the spine. In another example, orthopedic fasteners can be used tofix the location of a spinal spacer once the spacer is implanted betweenadjacent vertebral bodies. In yet another example, fasteners can beanchored to a number of vertebral bodies to fasten a spinal rod in placealong a spinal column to treat a spinal deformity.

However, the structure of spinal elements presents unique challenges tothe use of orthopedic implants for supporting or immobilizing vertebralbodies. Among the challenges involved in supporting or fusing vertebralbodies is the effective installation of an orthopedic implant that willresist migration despite the rotational and translational forces placedupon the plate resulting from spinal loading and movement. Also, forcertain implants, having low profile characteristics is beneficial interms of patient comfort as well as anatomic compatibility.

Furthermore, over time, it has been found that as a result of the forcesplaced upon the orthopedic implants and fasteners resulting from themovement of the spine and/or bone deterioration, the orthopedicfasteners can begin to “back out” from their installed positioneventually resulting in the fasteners disconnecting from the implant andthe implant migrating from the area of treatment.

As such, there exists a need for a fastening system that provides forlow profile placement of the bone anchor or screws and provides amechanism where the fasteners are blocked to prevent the anchors from“backing out” of their installed position.

SUMMARY OF THE INVENTION

In a preferred embodiment, the present invention provides an anchorassembly that can be used for the fixation or fastening of orthopedicimplants to bone tissue. In particular, the present invention preferablyprovides a low profile variable angle or fixed angle fastener assemblythat is able to securely connect the orthopedic device to bone tissue.Furthermore, in a preferred embodiment, the present invention furtherprovides a fastener assembly having a locking mechanism that willquickly and easily lock the anchor assembly with respect to theorthopedic device.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred or exemplary embodiments of the invention, areintended for purposes of illustration only and are not intended tolimit, the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is an exploded perspective view of one embodiment of a fasteningassembly;

FIG. 2 is a cross sectional side view of the fastening assembly shown inFIG. 1; and

FIG. 3 is schematic cross sectional side view of a prior art anchorsystem.

DETAILED DESCRIPTION OF THE INVENTION

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

With reference to FIGS. 1 and 2, a preferred embodiment of a fasteningassembly 10 is illustrated. The fastening assembly 10 preferablyincludes a fastener 12, a polyaxial locking head 24 and a lockingmechanism 14. The fastening assembly 10 is preferably constructed fromany biocompatible material including, but not limited to, stainlesssteel alloys, titanium, titanium based alloys, or polymeric materials.Although the fastener 12 will be discussed in the context of anorthopedic screw, it is contemplated that the fastener 12 can be anytype of fastening element including, but not limited to, a hook, a pin,or a nail.

In a preferred embodiment, the fastener 12 includes, concentric to alongitudinal axis 16, a head portion 18, a neck portion 20 and a shankportion 22. The head portion 18 connects to the shank portion 22 throughthe neck portion 20. The neck portion 20 of the fastener 12, preferably,integrally connects the head portion 18 with the shank portion 22. Thediameter of the neck portion 20 is preferably dimensioned to match aminor diameter of the fastener 12. By having the diameter of the neckportion 20 dimensioned at least as large as the minor diameter of thefastener 12, the overall rigidity and strength of the fastener 12 isincreased.

In a preferred embodiment, the shank portion 22 of the fastener 12includes a shaft 23 surrounded at least in part by a thread portion 25.The diameter of the shaft 23 is the minor diameter of the fastener 12.In a preferred embodiment, the diameter of the shaft 23 remainsgenerally constant from a proximal end of the shaft 23 toward a distalend of the shaft 23. The constant diameter of a majority portion of theshaft 23 allows for optimal fastener positioning when the fastener 12 isinserted into a predetermined area in the bone tissue. The constantdiameter also allows for varying the depth positioning of the fastener12 in the bone. For example, if a surgeon places the fastener 12 intobone tissue at a first depth and decides the placement is more optimalat a second, shallower depth, the fastener 12 can be backed out to thesecond depth and still remain fixed in the bone. In another embodiment,the diameter of the shaft 23 may vary along its length, includingincreasing in diameter from the proximal end to the distal end ordecreasing in diameter from the proximal end to the distal end.

With continued reference to FIGS. 1-2, the thread portion 25 surroundingthe shaft 23 extends, in a preferred embodiment, from the distal end ofthe shaft 23 to the neck portion 20. In another preferred embodiment,the thread portion 25 may extend along only a portion of shaft 23. Thethread portion 25 is preferably a Modified Buttress thread but thethread can be any other type of threading that is anatomicallyconforming, including, but not limited to Buttress, Acme, Unified,Whitworth and B & S Worm threads.

In a preferred embodiment, the diameter of the thread portion 25decreases towards the distal end of the fastener 12. By having adecreased diameter thread portion 25 near the distal end of the fastener12, the fastener 12 can be self-starting. In another preferredembodiment, fastener 12 may also include at least one flute to clear anychips, dust, or debris generated when the fastener 12 is implanted intobone tissue.

As best seen in FIG. 1, in a preferred embodiment, at least a portion ofthe head portion 18 of the fastener 12 has a generally spherical shapeand is preferably surrounded by the polyaxial locking head 24. Inanother preferred embodiment, the polyaxial locking head 24 includes atleast one extension 26, but, preferably includes two extensions 26; eachextension 26 being located diametrically opposite to the other on thepolyaxial locking head 24. Preferably, also located on polyaxial lockinghead 24 is at least one, but preferably two, notches or openings 28. Thenotches 28 are configured and dimensioned to correspond with the end ofa driving instrument (not shown) designed to engage the polyaxiallocking head 24. This engagement allows a user to manipulate thepolyaxial locking head 24 through the driving instrument. Similarly, thehead portion 18 of the fastener 12 also preferably includes a cavity oropening 30 configured and dimensioned to correspond with the end of thesame driving instrument or a separate driving instrument (not shown)designed to engage the fastener 12. This engagement allows a user todrive the fastener 12 into bone tissue and otherwise manipulate thefastener 12.

Turning back to FIGS. 1 and 2, the generally spherical shape of the headportion 18 is configured and dimensioned to be received within acorrespondingly shaped cavity 32 in the polyaxial locking head 24. Theshape of the head portion 18 and the correspondingly shaped cavity 32allows the fastener 12 to pivot, rotate and/or move with respect to thepolyaxial locking head 24. It should be noted that the head portion 18and the cavity 32 are dimensioned such that the head portion 18 cannotbe removed or otherwise disengaged from the cavity 32 of the polyaxiallocking head 24. In another embodiment, instead of allowing the fastener12 to pivot, rotate and/or move with respect to the polyaxial lockinghead 24, the head portion 18 and the correspondingly shaped cavity 32may be configured and dimensioned to keep the fastener 12 in a fixedposition. In a preferred embodiment, the head portion 18 may includetexturing 35 that extends along at least a portion of the head portion18. The texturing 35 on the head portion 18 provides additionalfrictional surfaces which aid in gripping the fastener 12 and holdingthe fastener 12 in place with respect to the polyaxial locking head 24.

In an exemplary use with an orthopedic device, the fastener 12 with thepolyaxial locking head 24 is received in an opening 34 in an orthopedicdevice 36. The opening is appropriately configured and dimensioned toreceive the fastener 12 and the polyaxial locking head 24 such that thepolyaxial locking head 24 can be rotated with respect to the device 36and the fastener 12 can be pivoted, rotated or moved until the desiredorientation is met with respect to the polyaxial locking head 24 and/orthe device 36. In a preferred embodiment, the opening 34 includes anupper opening 37 which receives the polyaxial locking head 24 and thehead portion 18 of the fastener 12 and a lower opening 39 which receivesthe shank portion 22. In a preferred embodiment, the upper opening 37also includes extensions 38 which are configured and dimensioned toreceive the extensions 26.

As mentioned above, in a preferred embodiment, the fastener assembly 10includes the locking mechanism 14. The locking mechanism 14 will lockthe fastener assembly 10 with respect to the orthopedic device 36thereby preventing the fastener assembly 10 from disengaging or “backingout” from the orthopedic device 36. The locking mechanism 14 furtherassists in engaging the fastener 12 and the polyaxial locking head 24with the opening 34 in the orthopedic device 36 in a low-profilearrangement. In a preferred embodiment, the locking mechanism 14includes extensions 26 of the polyaxial locking head 24, correspondingextensions 38 in the opening 34, and grooves 40. In a preferredembodiment, the grooves 40 extend from one extension 38 to the otherextension 38 and are generally radial. Preferably, the grooves 40 arelocated between the upper surface 42 and a lower surface 46 of thedevice 36.

In an exemplary use of the fastener assembly 10 with the orthopedicdevice 36, the orthopedic device 36 is first oriented and placed in thearea of treatment. The orthopedic device 36 is then fastened to the bonetissue via at least one fastener assembly 10 which is received in atleast one opening 34 of the orthopedic device 36. More specifically,looking at FIGS. 1-2, in a preferred embodiment, the fastener 12 and thepolyaxial locking head 24 are received in opening 34 such that the shankportion 22 passes through the lower opening 39 and the polyaxial lockinghead 24 and head portion 18 are receiving and seated in the upperopening 37. The fastener 12 via notch 30 can then be driven into thebony tissue. As best seen in FIG. 2, when received in the opening 34,the polyaxial locking head 24 and the fastener 12 are received in a lowprofile manner. In other words, regardless of the position of fastener12, even when the fastener 12 is rotated, pivoted, or otherwise moved,the head portion 18 of the fastener 12 will not breach the plane definedby an upper surface 42 of the device 36. This is in contrast to priorart systems, one of which is shown in FIG. 3, where the head of afastener will breach the plane defined by the upper surface of theorthopedic implant. This is particularly true when the fastener isinstalled at a steep or sharp angle.

Once the fastener assembly 10 is seated in the cavity 34, the fastenerassembly 10 can be locked in the opening 34 by actuating the lockingmechanism 14. In a preferred embodiment, a user actuates lockingmechanism 14 by rotating the polyaxial locking head 24 via notches 28 ina first direction. The rotational movement causes the extensions 26which are seated in the extensions 38 to rotate into the grooves 40.Although only one groove is shown in broken lines in FIG. 1, it shouldbe understood that there are two sets of diametrically opposed grooves40 which extend in an annular fashion between the extensions 38. In apreferred embodiment, the grooves 40 include a stop to provide feedbackto the user that the polyaxial locking head 24 has been fully rotatedand the locking assembly 14 is engaged. In another preferred embodiment,the grooves 40 change in dimension so that the protrusions 26 can becaptured in grooves 40 in an interference manner as the polyaxiallocking head 24 is rotated. In yet another preferred embodiment, thegrooves 40 include protrusions that provide audible and tactile feedbackto the user as the user locks the fastening assembly 10.

With the polyaxial locking head 24 rotated, the fastener assembly 10 islocked in the opening 34 since the protrusion 26 in the grooves 40prevents the polyaxial locking head 24 and fastener 12 from disengagingor “backing out” from the opening 34. If a user wants to unlock thelocking mechanism 14 and remove fastener assembly 10 from the opening 34of device 36, the user would simply rotate the polyaxial locking cap 24via notches 28 in a second direction thereby rotating the protrusions 28out of grooves 40 and into extensions 38. At that point the lockingmechanism 14 is disengaged and the fastener assembly 10 can be removedfrom the opening 34 of the orthopedic device 36.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. An orthopedic device for implantation into bonetissue, said orthopedic device comprising: a bone plate having anunthreaded opening extending from a most upper surface of the bone plateto a most lower surface of the bone plate, wherein the bone platefurther comprises at least one groove in communication with the opening;a fastener assembly configured to be inserted into the bone plate,wherein the fastener assembly comprises a locking head and a fastener,wherein the fastener is received in an unthreaded opening formed in thelocking head; wherein the fastener assembly communicates with the atleast one groove to prevent backout of the fastener assembly from thebone plate; and wherein the height of the locking head is configured toextend from the most upper surface of the bone plate to the most lowersurface of the bone plate.
 2. The orthopedic device of claim 1, whereinthe fastener further comprises a head portion, a neck portion, and ashank portion.
 3. The orthopedic device of claim 2, wherein the headportion of the fastener is received in the opening formed in the lockinghead.
 4. The orthopedic device of claim 1, wherein the locking headcomprises an extension configured to engage the at least one groove. 5.The orthopedic device of claim 4, wherein the extension extends from aspherical surface of the locking head.
 6. The orthopedic device of claim1, wherein the locking head comprises one or more notches for receivinga driving instrument therein.
 7. The orthopedic device of claim 1,wherein the fastener is capable of pivoting and/or rotating relative tothe locking head.
 8. The orthopedic device of claim 1, wherein thelocking head comprises a spherical opening formed therein.
 9. Theorthopedic device of claim 1, wherein the at least one groove is radial.10. The orthopedic device of claim 1, wherein the at least one grooveincludes a stop.
 11. An implant for fixation into bone tissue, saidimplant comprising: an orthopedic device comprising an unthreadedopening extending from a most upper surface of the orthopedic device toa most lower surface of the orthopedic device, wherein the orthopedicdevice comprises one or more grooves in communication with the opening;a fastener assembly configured to be received into the orthopedicdevice, wherein the fastener assembly comprises a locking headcomprising a pair of extensions; and wherein the fastener assembly isconfigured such when the fastener assembly is rotated within theorthopedic device, the pair of extensions are received in the one ormore grooves of the orthopedic device to thereby prevent backout of thefastener assembly from the orthopedic device, wherein the height of thelocking head extends from the most upper surface of the orthopedicdevice to the most lower surface of the orthopedic device, wherein thefastener assembly further comprises a fastener that is received in anunthreaded opening of the locking head.
 12. The implant of claim 11,wherein the orthopedic device comprises a bone plate.
 13. The implant ofclaim 12, wherein the one or more grooves are in communication with theopening.
 14. The implant of claim 11, wherein the opening of the lockinghead is spherical.
 15. The implant of claim 11, wherein the locking headcomprises one or more notches for engaging a driving instrument.
 16. Theimplant of claim 11, wherein the one or more grooves are radiallyformed.
 17. The implant of claim 11, wherein the fastener assembly isretained within the orthopedic device such that an upper most surface ofthe fastener assembly remains below an upper most surface of theorthopedic device.
 18. The implant of claim 17, wherein the orthopedicdevice comprises a plate.
 19. The implant of claim 17, wherein thefastener assembly further comprises a fastener, wherein the fastener isreceived within an opening of the locking head and is rotatable relativeto the locking head.